Peracid bleaching agents have become an important alternative to chlorine or bromine bleaching agents in automatic dishwashing formulations. However, the pure form of many of these peracid bleaches may be insufficiently stable to be formulated without cogranulating the bleaches with an exotherm control agent. (See U.S. Pat. No. 4,100,095 (P&G)). These exothermic control materials absorb and dissipate any energy released from the peracid during slow decomposition at elevated temperatures and hinder any temperature rise of the cogranules. This prevents a runaway decomposition from occurring and eliminates the safety hazard at these temperatures.
Many of these agents are known and are reported in the literature. They consist of two types of compounds.
The first type consist of inorganic salt hydrates which release some of their waters of hydration at temperatures below the decomposition temperature of the peracid. These include hydrated materials such as magnesium sulfate, calcium sodium sulfate, magnesium nitrate, and aluminum sulfate (See Neilsen, U.S. Pat. No. 3,770,816). While these hydrated materials are able to supply water to quench the exothermic reaction, they suffer from several defects. These defects include:
1. The hydrated salts maintain sufficient vapor pressure of water in the presence of the peracid to increase the loss of available oxygen.
2. The loss of water to the surroundings due to high vapor pressure reduces the amount of exotherm control after lengthy storage periods.
3. Many of the hydrated salts contain high levels of metal ions which increase the loss of available oxygen during the storage and shelf life of the product and decrease the peracid performance in the wash solution.
The second type of exotherm control agent consists of nonhydrated compounds which decompose at temperatures below the decomposition temperature of the peracid to liberate water. These compounds provide the same exotherm control benefits of the hydrated salts while overcoming the aforementioned problems. Materials of this type include boric acid, malic acid, maleic acid, succinic acid, phthalic acid, and azelaic acid (See Hutchins et al., U.S. Pat. No. 4,100,095; and Burns, U.S. Pat. No. 4,686,063). Due to their acidic nature these compounds also create a slightly acidic environment for the peracid particles during storage which will lower hydrolysis rates and increase the stability of the peracid. A particularly useful material in this respect has been boric acid due to its high weight effectiveness.
Although all the materials in the aforementioned second group of compounds have been found to be effective as exotherm control agents, it has been observed that they decrease the effectiveness of the pure form of peracid bleaching agents. All of the compounds have rather low solubilities and dissolve slowly in the wash solution.
This results in a slow dissolution of the peracid granule which decreases the performance of the bleaching agent. This lessened performance is particularly pronounced in colder temperatures and for coated granules which provide a delayed release of the peracid.
It has been found in the present invention that an improved exotherm control compound will provide improved dissolution and an acidic environment within the granule, be devoid of metal ions, and supply water at temperatures below the decomposition temperature of the peracid to control exothermic decomposition.
Accordingly, it is an object of the present invention to provide a composition containing a peracid compound having improved dissolution properties while maintaining good exothermic control.
As used herein, all percentages and ratios are by weight unless otherwise specified.